Re: Hardware Project

[david@uow.edu.au (David Wilson)]

"Terence J. Boldt" <apple2@cgocable.net> writes:
>Write the controlling code for it and squeeze it into 256 bytes.  Make it
>work with ProDOS.

>I need to know how ProDOS accesses a block device for read and write.  I
>know about all the ID and info bytes required in ROM (thanks Dave Wilson),
>but what do I need to handle as far as calls from ProDOS to my card?

Cn01	20
Cn03	00
Cn05	03
Cn07	00	If Smartport, bootable on enhanced //e and //gs
	3C	If not Smartport and bootable on ][+, //e and //gs.
	other	bootable only on enhanced //e and //gs
CnFC/D	XXXX	total blocks on disk
	0000	if STATUS call will return # of blocks
CnFE	XX	status byte
		bit 7		removable medium
		bit 6		device is interruptable
		bits 5 & 4	number of volumes supported (0..3 according to
				Apple docs - I think that this represents 1..4)
		bit 3		device supports FORMAT
		bit 2		device supports WRITE
		bit 1		device supports READ	(must be set)
		bit 0		device supports STATUS	(must be set)
CnFF	XX	low byte of entry point to driver
	00	Disk II with 16 sector ROM - internal driver used
	FF	Disk II with 13 sector ROM - not supported

The first 4 bytes listed above can be taken care of by:

Cn00	CMP	#$20
	CMP	#$00
	CMP	#$03
	CMP	#$3C

The driver code is passed the following:

0042	command		0 = STATUS, 1 = READ, 2 = WRITE, 3 = FORMAT
0043	unit#		bit 7		drive (0 = 1st, 1 = 2nd)
			bits 6-4	slot #
			bits 3-0	unused
0044/5	buffer		pointer to 512 byte buffer
0046/7	block#		number of block to read/write, ignored for status/format

The return status is in the A register and carry is set if an error occured.

Errors such as I/O Error ($27), No Device Connected ($28) and Write Protected
($2B) should be implemented.

If you support 3 or 4 volumes then the card has to go in slot 5 and you
have to handle being passed calls for slot 2 (by adding 2 to the drive number
passed in $43).

To have a bootable card, the code starting at Cn00 should load block 0
of drive 0 into memory at $0800. If this succeeds, check that $0800 contains
a $01. If so, jump to $0801. If any of this fails, put a message up on the
screen saying so. If you want to be really nice you can jump back to SLOOP
in the monitor (after adjusting the slot number) and the system will keep
scanning for a bootable device.

--
David Wilson  School of IT & CS, Uni of Wollongong, Australia  david@uow.edu.au